Fluorine-18 labeled arachidonic acid ([18F]ArA) uptake in LuCaP xenografts

LuCaP xenografts were processed and cultured as organoids as described previously [31]. Organoid identity was validated every 6 months by STR profiling (Laragen). Organoids were cultured for 7 days in 2% Matrigel, collected, washed with PBS, then resuspended in 1 mL of Beshiri’s Modified Clevers Media [31] in duplicate tubes for in vitro [¹⁸F]ArA uptake assays.

[¹⁸F]ArA was prepared following as previously described with minor modifications [57]. Briefly, the tosylate precursor was heated with [¹⁸F]TBAF in acetonitrile at 120 °C for 20 min followed by hydrolysis with potassium hydroxide (120 °C for 10 min) to produce 20-[¹⁸F]ArA. The overall radiochemical yields were 15–24% (uncorrected, n > 6) with a molar activity of 59–163 GBq/µmol (n > 6).

Organoid cultures were radiolabeled with 2 μCi [¹⁸F]ArA in BMCM for 120 min at 37 °C/5% CO₂, washed twice with PBS to remove residual unincorporated [¹⁸F]ArA, and resuspended in 1 mL trypsin as a single-cell suspension. Cells were counted using acridine orange/propidium iodide cell counting dye. [¹⁸F]ArA uptake was determined by PerkinElmer 2480 Wizard3 Gamma Counter. For each sample, percent uptake per 10⁶ live cells was calculated as follows: